1. Field of the Invention
This invention relates to a clean tunnel structure, in which materials and articles to be conveyed in a clean tunnel are kept constantly in a clean condition.
2. Description of the Prior Art
To convey semiconductors or the like in a clean room or tunnel, a light-weight self-running truck having a casing with a cover plate is employed. The semiconductors must always be kept in a clean condition. FIG. 5 shows a conventional clean tunnel 1 which is used for connecting a plurality of neighboring clean rooms R. FIG. 6 shows another conventional clean tunnel 1 which is connected to an environmental chamber E, a line-type clean bench L and a clean booth B. The clean tunnel 1 communicates with some places other than the clean rooms, so that clean air must be filled therein. Disposed in the clean tunnel is a conveying means as shown in FIGS. 3 and 4. The conveying means is a self-running truck.
The clean tunnel 1 is provided with a frame body 2 of a rectangular section having an air flow passage 2k at its upper part and an air filter 3 under the air flow passage 2k. Any type of air filter having a high efficiency may be selected. On the other hand, two travelling rails 4 are laid in a longitudinal direction on a center of a bottom plate 2b of the frame body 2. Further, disposed between the two rails 4 are a conventional signal supply cable and a conventional power supply cable, both of which are not illustrated.
A plurality of air inlets 5 spaced from each other are disposed along a side wall 2s of the air flow passage 2k and a plurality of air outlets 6 spaced from each other are disposed on the bottom plate 2b so as to correspond to the plurality of air inlets 5. Numeral 7 is a transparent plastic plate mounted between both ends of the side wall 2s. A user can see the travelling condition of a self-running truck 8 and other things.
The self-running truck 8 (hereinafter called briefly "truck") for conveying e.g. the semiconductor wafers is driven automatically on the rails 4 by power supply of the power supply cable. It comprises driving means 8r for driving wheels 8w, mechanical means 8k having braking means, starting means or the like, a casing 8c for conveying articles, and a cover plate 8f for covering the casing 8c.
Air supplied into the passage 2k by way of the air inlet 5 from an air blower (not illustrated) is filtered by the air filter 3, and a clean air flows as a laminar layer downwardly with an air flow speed of 0.5 m/s. Thus the interior 2t of the tunnel 1 is fully filled with the clean air. It is discharged outside through the air outlet 6 by driving an air discharge blower (not illustrated).
The materials, parts and articles to be conveyed are delivered to respective automatic processing stations where robot devices are disposed, and must be subject to automatic processing. At the processing stations, these materials, parts, and articles must be exposed outwardly with no covering. Otherwise, a suitable processing cannot be carried out effectively.
Further, according to a conventional clean tunnel, as the speed of the truck 8 is increased, air vortex flow occurs behind the truck 8, thereby to form dust as a result of contact between the wheels of the truck 8 and the rails 4. Because of this, the air purification degree within the tunnel is decreased and those materials, parts and articles are polluted. Thus, the running speed of the truck 8 must be restricted, so that its conveying efficiency is reduced.